1. Field of the Invention
The invention relates to a self-propelled robot adapted for example to clean and monitor a work area, the robot memory containing a map of the work area for ensuring a proper travel path of the robot.
2. Description of the Prior Art
Generally, there is disclosed in Japanese Laid-Open patent application No. 4-365104 an apparatus for producing an optimal travel path of a self-propelled robot, as shown in FIG. 1. The apparatus includes a map storage portion 4 for memorizing a map having the cleaning (work) areas and obstacles marked throughout an overall work area, a map producing/updating portion 8 for providing the map with information about environmental conditions and updating the map stored in said map storage portion 4, a travel path searching portion 5 for finding a travel path to a target point by utilizing the map stored in the map storage portion 4, and a travel path producing portion 7 for finding obstacle avoidance paths by utilizing the map stored in the map storage portion 4.
The robot equipped with the above optimal path finding apparatus 9 receives a current position of the robot from a self position recognition portion 2, a position of the target point from an instruction producing portion 1, and data containing information about surrounding obstacles from an obstacle recognition portion 6.
Based upon the received information, the robot may be moved along a planned travel path delivered to a driving portion 3 through the path searching portion 5 or the travel path producing portion 7.
Furthermore, the map producing/updating portion 8 produces a map showing the conditions around the robot on the basis of the information about obstacles received from the obstacle recognition portion 6 when the robot moves and the current position from the self position recognition portion 2 and, based upon the thus-produced map, updates the map showing the overall work place which is stored in the map storage portion 4.
Such a conventional optimal path finding apparatus is not required to use all information about the work area during an initial operation, and is able to define more effective paths every time the finding procedures are performed and to cope with the change of the work area. The apparatus, however, has to move the robot by using the positions of the target point and the robot and the information about the presence of the obstacles, and to update the stored map for overall work area based upon the produced map according to the current position and the presence of the obstacles. This results in the use of a large memory capacity.
In addition to the above-mentioned technique, another prior art is disclosed where the tasks can be effected only by information about the work environments. In such a technique, a given work area is divided into cell units, each having a constant size, of which each cell has necessary information about the presence of the obstacles. The apparatus is provided with signal emitting devices(for example, ultrasonic or infra-red signal generating devices) mounted on the surfaces of the walls in the work area. The robot is able to receive the emitted signals through a receiver located on a predetermined position of a main body of the robot, and travel alongside the wall surface or freely travel within the work area during the initial operation of the robot.
At this time, when a signal emitted from the signal emitting devices, which represents a location of the signal emitting device, is received through the receiver, the robot analyzes and automatically creates the environmental map which is used to clean or monitor.
The above-mentioned technique, however, utilizes only the information about the environment of the work area. Thus, it is difficult for the robot to accurately recognize its current position, and the apparatus also requires a larger memory capacity due to the storage of the information about cells of the same size dividing the given work area.
Furthermore, it is required to have separate external devices for emitting ultrasonic or infra-red waves carrying the positional information, resulting in the complex structure and complicated installation of the apparatus.
Also, due to the quality and state of the floor surface, sliding of the driving wheels of the robot may occur, which prevents the robot from accurately reaching the signal emitting device. Thus, in a case where the receiver does not receive the emitted signals, the robot continues to move to the left or to the right, and vice versa, in order for the receiver to receive the emitted signal. This requires a longer time for the robot to find the current position thereof.